Metallocene catalysts are a new class of catalysts which are gradually replacing Ziegler catalysts for the polymerization of olefins, such as ethylene and propylene. A metallocene catalyst typically consists of a transition metal compound bonded to at least one ligand that contains a cyclopentadienyl ring. While such catalysts are more expensive than Ziegler catalysts, they are much more efficient. Recently, catalysts containing boraaryl and azaborolinyl rings have been proposed as alternatives to metallocene catalysts.
Typically, unsupported catalyst systems have too small a particle size for commercial use. Supported catalysis systems are characterized by larger particle sizes and offer improved catalytic efficiency over their unsupported counterparts. Supported catalysis systems further are generally more stable.
It is often difficult to control the amount of catalyst loaded onto the supports of the prior art. This is unfortunate in light of the high manufacturing costs of the catalyst itself. In addition, the supported catalysis systems of the prior art exhibit a high degree of self-deactivation; presumably caused by close proximity of the active sites on the support. A need therefore exists for more cost efficient catalysis systems which exhibit a diminished risk of deactivation.